[110.12] A Search for Diffuse X-Ray Emission from OB Associations

F. Buls, J.-P. Caillault (University of Georgia)

We report on our search for diffuse emission from OB associations observed
with the Einstein
IPC. Our sample includes
nine associations; only two, Ser~OB2 and Car~OB2, show any evidence for
significant unresolved extended emission. Using extinctions and distances
taken from Humphreys (1987) and assuming a RS thermal bremsstrahlung emission
spectrum with T $\sim$ 6~x~10$^6$~K, we find that the X-ray luminosities of
the two regions range from $\sim$~10$^{32}$ to $\sim$~10$^{33}$ergs~s$^{-1}$,
comparable to the value
claimed by Fabian \& Stewart (1983) for a similar region in Cep~OB3.
Although the emission could be truly diffuse (i.e., the result of
non-radiative heating of the ambient gas
by the association members), we consider the possibility of unresolved point
sources as still tenable. To further elucidate this latter possibility we
have ROSAT HRI observations planned for next year.
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Partial support for this project has been provided by NASA through grant NAG8-148.